Steam generating unit



Oct. 9, 1962 H. B. OPLADEN STEAM GENERATING UNIT Filed June 27, 1960 INVENTOR. flein B. 0PZ 1CZ67Z BY My w o neg ited tts This invention relates to steam generating apparatus, and more particularly to apparatus arranged to produce steam for the operation of a turbine-generator set.

It is common practice in power plants to obtain the energy from steam by passing it through two turbines, one of which is a low-pressure turbine and the other of which is a high-pressure turbine, and returning the steam to the steam generating unit for reheating between the two stages. It has been suggested that the second stage, which is a low pressure turbine and requires a relatively inexpensive construction, be made considerably larger in capacity than the low-pressure turbine so that it is capable of operating during high load periods with a considerably greater amount of steam flowing through it than the high-pressure turbine. Since this requires that more steam be returned from the reheater portion of the steam generating unit than originally emerged from the superheater, a considerable problem is presented. One way of doing this, of course, would be to provide a small supplementary steam generating unit to provide the low-pressure turbine with the extra required steam. The added auxiliary equipment and so on, however, would to a great extent offset the savings which prompted one to provide the large capacity low-pressure turbine in the first place. These and other difficulties experienced with prior art devices of this kind have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit capable of supplying considerably larger amounts of steam from the reheater than from the superheater.

Another object of this invention is the provision of a once-through, forced-flow boiler capable of supplying peak load steam to a large size, low-pressure turbine operating with a small size high-pressure turbine.

A further object of the present invention is the provision of a steam generating unit in which the economizer surfaces are used as a low temperature reheater section during peak load conditions.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawing in which:

The single FIGURE shows a somewhat schematic view of a power plant incorporating the principles of the present invention.

Referring to the drawing, it can be seen that the power plant, indicated generally by the reference numeral '10 is provided with two feed water pumps 11 which are connected to force water through a high-pressure pre-heater 12 which is followed by a feed water regulation valve 13. In the backpass of the steam generating unit associated with the power plant is situated a primary reheater section 14. A control 15 is connected to the valve 13 for the regulation thereof. A throttling valve 16 is located in the pipe leading from the valve 13 to an inlet header 17 at the lower part of the main furnace of the steam generating unit. Another line leads from the valve 13 to an economizer inlet header 18 associated with the economizer of the steam generating unit, which economizer is separated at least in part from the pass in which the primary re-heater section 14 is located. The economizer 19 has a lower portion which extends entirely across the backpass of the steam generator and an upper portion which extends only in a passage separated by a baffie 20 from the passage in which the primary reheater section 14 lies. The high-temperature section of the economizer 19 is provide-d with platens which lie in the upper convection pass of the steam generating unit and are connected to a collecting header 21 which is connected to a spill-over valve 22 which will be described more fully hereinafter. The feed water pumps 11 are also connected by a line to a spray-type desuperheater 23 and the pipe has a spray water control valve 24 connected from the line. A con necting pipe 25 leads from the collecting header 21 to a steam mixer 26 into which the steam generating tubes in the evaporation zone 28 of the boiler discharge. An automatic check-valve 27 is located in the connecting pipe 25. When the pipe 25 is connected not only with the inlet header 17 but with the intermediate portion of the evaporation zone 28 the upper portion of the evaporation zone is connected to the steam mixer 26, the output of which is connected to the radiant superheater 29. The output end of this superheater is connected to the final superheater 30 which is in the form of radiant platens located in the upper part of the furnace. The final section of reheater tubes are formed as platens 31 which are also located in the upper part of the furnace. The high pressure piping 32 leads steam from the furnace superheater 30 through a throttle valve 34 to the high-pressure turbine 35. In a similar manner, pressure piping 33 leads from the output of the final section of reheater platens 31 to the low-pressure turbine 36, the turbines 35 and 36 being connected in the usual way to an electrical generator 37. There is a wattmeter 38 which is connected to provide a signal to a fuel controller '39 as Well as a valve controller 41. A suitable condenser 40 follows the lowpressure sections of the turbine in the usual manner and the condensed steam is led to a hot well 42 which is connected to the inlet sides of the pumps 11. -'Ihe turbines are provided with a governor 43 which is connected in a controlling manner to the throttle valve 34. As is clear, suitable controls are provided for the pumps 11 so that flow is maintained at predetermined rate. In the same way the flow through the pipe leading to the economizer inlet header 18 and to the steam desuperheater 23 are regulated and maintained in a proper ratio by orificetype flow measuring device in these pipes which operate through the control 15 to regulate the valve 13 so that the amount of water supplied to the desuperheater is in proportion to the amount of water which passes through the forced-flow once-through boiler. The controller 41 receives signals from the spill-over valve 22 which is connected between the collecting header 21 and the inlet to the final section of reheater platens 31; it is connected also to the wattmeter 38 to receive a signal and to control the flow of water through the throttling valve 16 leading to the inlet header 17. The desuperheater control valve 24 is controlled from temperature readings taken in the superheater piping 32, while the division of flow of gases through the passes in the backpass of the boiler is regulated by dampers under the control of temperature measurements taken in the reheater piping 33. The fuel controller 39 receives signals from the wattmeter 38 and also from pressure-drop measurements taken around the throttle valve 34 in the conventional manner.

The operation of the apparatus will now be readily understood in view of the above description. Feed water is supplied by the high-pressure feed Water pumps 11 and, after passing through the high-pressure preheater 12, the feed Water enters the economizer inlet header 18, after passing through the feed water regulation valve 13. After traveling through the economizer 19 and its hanger tubes, the water flows through tube platens to the collecting header 21. It then passes through the connecting pipe 25 through the inlet header 17 into the evaporation zone 28. The slightly superheated steam then enters the steam mixer 26 in which steam from parallel circuits will mix uniformly before entering the radiant superheater 29. The superheated steam leaves the superheater 29 and flows through the spray-type desuperheater 23 to the final superheater 30. Steam of the correct temperature and pressure passes through the pipe 32 and the throttle valve 34 to the high-pressure turbine 35.

As has been stated above, the reheater consists of two sections, a primary section 14 located in a regulating pass and a final section of radiant tube platens 31. The steam returns from the high-pressure turbine 35, flows through the primary reheater section, where its temperature is controlled by gas flow dampers. After receiving its final temperature in the radiant section 31, the steam enters the low-pressure turbine 36 after traveling through the pipe 33. After passing through the low-pressure turbine 36, the steam is exhausted through the condenser 40 and passes into the hot well 42 from which it is fed to the feed pumps '11.

A change in fuel input tends to change steam temperature, but steam temperature is maintained at a constant value in the present case by the desuperheater 23 under the influence of the control 24. The steam output of the unit is controlled by the fuel input. The fuel controller 39 receives its impulse from the wattmeter 38. The boiler control maintains a constant ratio of spray water and feed water flow. This control system is the subject of my co-pending patent application Serial No. 38,793 filed June 27, 1960. This constant ratio is, of course, maintained by the control 15. The steam temperature thus controls both spray water and feed water flow.

The present boiler is designed to produce larger quantities of low-pressure steam than that normally required for a conventional single reheat plant, but only during a period of higher or peak demand. For a normal load condition the boiler performs as a conventional reheat unit. Under peak load part of the economizer surface of the boiler is converted to reheater surface, while another portion of the initial economizer surface becomes evaporating surface. When a higher than normal load demand is encountered, the wattmeter 38 through its connection to the fuel controller 39 calls for increased burn ing rate. The higher rate of furnace heat released tends to increase the final steam temperature beyond its predetermined value and, because feed water flow is controlled from steam temperature, an increase in feed Water flow is automatically called for by an impulse sent to the feed valve 13. The increase in power demand above normal automatically opens the throttling valve 16 which permits a portion of the feed water to flow directly to the evaporating section of the boiler, thus by-passing the evaporation within the economizer. This results in eventual heating of the steam thus generated in the economizer to a predetermined high value; when this temperature is reached, the spill-over valve 22 permits steam generated in the economizer to flow into the reheater. This valve performs as a pressure-reducing valve so that the correct predetermined reheater pressure is maintained. The reheater flow is, thus, increased by the quantity of steam generated in the upper section of the economizer and more than normal low pressure steam of the correct temperature is being supplied to the low-pressure section 'of the turbine.

The connecting line 25, which normally connects the economizer with the evaporating zone of the boiler, contains the automatic check-valve 27. When the spill-over valve 22 is opened, the pressure within the pipe line 25 is greatly reduced so that the check valve 27 closes to prevent feed water from flowing through this pipe line.

W=constant P That is, the steam pressure entering the turbine nozzle changes linearly with the load. To operate a boiler with variable pressure over the entire load range it is not necessary to control the turbine with regulating valves. The turbine speed is determined by the equation:

wherein Ah=enthalpy of steam; W=steam Weight; and I=electrical energy. When the network calls for more load, the speed of the turbine generator tends to drop. The generator 37 must maintain a constant speed and, therefore, the governor '43 of the turbine calls for more steam by its control over the throttle valve 34. It would be, of course, possible to send a signal from the governor 43 directly to the fuel input control 39, but the lag in time in using this type of control is prohibitive and for this reason the throttle valve 34 is placed between the boiler and the turbine. This valve holds a constant pressure drop across itself over the entire load range. If the governor calls for more steam, this throttle valve 34 opens suddenly and pressure and steam weight at the turbine inlet increases, so that the boiler acts as an accumulator and overcomes the delay time of the firing equipment. It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is: 1. In a power plant having a high-pressure turbine and a low-pressure turbine having a greater capacity than the 50 high-pressure turbine, a steam generating unit having an economizer, an evaporative zone, a superheater, and a reheater, the output end of the reheater being connected to the low-pressure turbine, feed water lines connected to the input end of the economizer and to the evaporative 55 zone of the unit, a normally-inoperative means connecting the output end of the economizer to the input end of the reheater, and means responsive to peak load demand to render the first-named means operative.

2. In a power plant as recited in claim 1, a check valve 60 located in a line connecting the evaporative zone to the economizer serving to inhibit flow of fluid from the economizer to the evaporative zone when the said normallyinoperative means is operative.

3. A steam generating unit for use with a high-pressure 5 turbine and a low-pressure turbine, wherein the low-pressure turbine has substantially greater capacity than the high-pressure turbine, comprising an elongated combus tion chamber having a lateral convection pass at one end leading to an elongated backpass, a baffle dividing the 70 backpass into two parallel passages, a primary reheater in one of the said passages, an economizer in the other of the said passages, a secondary reheater consisting of radiant tube platens located at the said one end of the combustion chamber, the reheaters being connected in series with one 75 another and with the low-pressure turbine, an evapora- X constant tion zone consisting of tubes arranged on the surfaces of the combustion chamber, a superheater having radiant tube platens located in the said one end of the combustion chamber, the evaporation zone and the superheater being connected in series with one another and with the highpressure turbine, a spillover valve connected between the output of the economizer and the inlet of the secondary reheater, and a controller for opening the spillover valve when the load on the unit exceeds a predetermined value.

4. A once-through, forced-flow steam generating unit for use with a high-pressure turbine and a low-pressure turbine, wherein the low-pressure turbine has substantially greater capacity than the high-pressure turbine, comprising an elongated combustion chamber having a lateral convection pass at one end leading to an elongated back-pass, a baffle dividing the back-pass into two parallel passages, a primary reheater in one of the said passages, an econornizer in the other of the said passages, a secondary reheater consisting of radiant tube platens located at the said one end of the combustion chamber, the reheaters being connected in series with one another and with the low-pressure turbine, an evaporation zone consisting of tubes arranged on the surfaces of the combustion chamber, feed water pumps supplying feed water to the economizer and the evaporation zone, valves regulating the division of water between the economizer and the evaporation zone, a superheater having radiant tube platens locat ed in the said one end of the combustion chamber, the evaporation zone and the superheater being connected in series with one another and with the high-pressure turbine, a spillover valve connected between the output of the economizer and the inlet of the secondary reheater, and a controller for opening the spillover valve when the load on the unit exceeds a predetermined value.

5. A steam generating unit for use with a high-pressure turbine and a low-pressure turbine, wherein the low-pressure turbine has substantially greater capacity than the high-pressure turbine, comprising an elongated compression chamber having a lateral convection pass at one end leading to an elongated backpass, a baflle dividing the backpass into two parallel passages, 21 primary reheater in one of the said passages, an economizer in the other of the said passages, a secondary reheater consisting of radiant tube platens located at the said one end of the combustion chamber, the reheaters being connected in series with one another and with the low-pressure turbine, an evaporation zone consisting of tubes arranged on the surfaces of the combustion chamber, a superheater having radiant tube platens located in the said one end of the combustion chamber, the evaporation zone and the superheater being connected in series with one another and with the highpressure turbine, a desuperheater located between the evaporation zone and the said radiant tube platens, a valve connected between a source of feed water and the desuperheater to regulate the flow of water to the desuperheater, a spillover valve connected between the output of the economizer and the inlet of the secondary reheater, and a controller for opening the spillover valve when the load on the unit exceeds a predetermined value.

6. A once-through, forced-flow steam generating unit for use with a high-pressure turbine and a low-pressure turbine, wherein the low-pressure turbine has substantially greater capacity than the high-pressure turbine, comprising an elongated compression chamber having a lateral convection pass at one end leading to an elongated backpass, a baffle dividing the backpass into two parallel passages, a primary reheater in one of the said passages, an economizer in the other of the said passages, a secondary reheater consisting of radiant tube platens located at the said one end of the combustion chamber, the reheaters being connected in series with one another and with the low pressure turbine, an evaporation zone consisting of tubes arranged on the surfaces of the combustion chamber, feed water pumps supplying feed water to the economizer and the evaporation zone, valves regulating the division of Water between the economizer and the evaporation zone, a superheater having radiant tube platens located in the said one end of the combustion chamber, the evaporation zone and the superheater being connected in series with one another and with the high-pressure turbine, a desuperheater located between the evaporation zone and the said radiant tube platens, a valve connected between the feed water pumps and the desuperheater to regulate the flow of water to the desuperheater, a spillover valve connected between the outlet of the economizer and the inlet of the secondary reheater, and a controller for opening the spillover valve when the load on the unit exceeds a predetermined value.

7. In a power plant having a high-pressure turbine and a low-pressure turbine having a greater capacity than the high-pressure turbine, a once-through, forced-flow steam generating unit having an economizer, an evaporation zone, a feed water pump supplying feed water to the economizer and the evaporation zone, valves regulating the division of water between the economizer and the evaporation zone, a superheater, a reheater, the output end of the reheater being connected to the low-pressure turbine, feed water lines connected to the input end of the economizer and to the evaporation zone of the unit, a normally-inoperative means connecting the output end of the economizer to the input end of the reheater, and means responsive to peak load demand to render the firstnamed means operative.

8. In a power plant having a high-pressure turbine and a low-pressure turbine having a greater capacity than the high-pressure turbine, a steam generating unit having an economizer, an evaporative zone, a superheater, a reheater, the output end of the reheater being connected to the low-pressure turbine, feed water lines connected to the input end of the economizer and to the evaporative zone of the unit, a desuperheater located between the evaporation zone and the superheater, a valve connected between a [feed water source and the desuperheater to regulate the flow of water to the desuperheater, a normally-inoperative means connecting the output of the economizer to the input end of the reheater, and means responsive to peak load demand to render the first-named means operative.

9. In a power plant having a high-pressure turbine and a low-pressure turbine having a greater capacity than the high-pressure turbine, a once-through, forced flow steam generating unit having an economizer, an evaporation zone, feed water pumps supplying feed water to the economizer in the evaporation zone, valves regulating the division of water between the economizer and the evaporation zone, a superheater, a reheater, the output end of the reheater being connected to the low-pressure turbine, feed water lines connected to the input end of the economizer and to the evaporation zone of the unit, a desuperheater located between the evaporation zone and the said radiant tube platens, a valve connected between the feed water pumps and the desuperheater to regulate the flow of water to the desuperheater, a normally-inoperative means connecting the output end of the economizer to the input end of the reheater, and means responsive to peak load demand to render the first-named means operative.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,433 Kuppenheimer July 8, 1952 2,685,280 Blaskowski Aug. 3, 1954 2,852,005 Buri Sept. 16, 1958 2,878,791 Lieberherr Mar. 24, 1959 

